There's also two different types of Philly Cheese Steak. There's the classic Philly Cheez Steak, which is basically sliced steak'ums cooked on the grilled with onions, with molten cheez whiz poured in. That's the kiosk-style philly, and is extremely popular - every third sidewalk food cart sells them, or did the last time I was in Philly. Then there's the "germantown" version, which uses sliced top round, white american cheese or provolone, onions, and green peppers. Both are Philly Cheese Steaks (Germantown is a section of Philadelphia).
There's a local variant here (I live in the Lehigh Valley), when you order a cheesesteak you it has tomato sauce, shredded roast beef, onions, peppers, white american cheese, and pickles. It's actually pretty good.